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Ref. No. [UMCES] CBL 2015-008
ACT VS15-01
4
At Chesapeake Bay the field deployment test was conducted over 30 days with a mean
temperature and salinity of 5.9
o
C and 12.8. The measured pH range from our 107 discrete
reference samples was 8.024 – 8.403. The CSI operated successfully over the entire 30 day
deployment with a measured range in ambient pH from 7.693 to 7.979. A programming error
initiated by ACT personnel during set-up resulted in the shutter being closed during every other
observation, so the useable number of observations was reduced from 2756 to 1378. No
comparative data with reference samples were lost due to this programming error. The average
and standard deviation of the measurement difference between the CSI and reference pH was -
0.398 ±0.040, with the total range of differences from -0.472 to -0.316.
At Lake Michigan the field deployment test was conducted over 29 days with a mean
temperature and salinity of 21.2
o
C and 0.03. The measured ambient pH range from our 98
discrete reference samples was 8.013 to 8.526. The CSI-pH operated continuously over 29 days
and generated 2680 observations with a range in ambient pH from 7.240 to 7.946. The average
and standard deviation of the difference between CSI and reference pH was -0.676 ± 0.109
(N=98), with a total range of -0.894 to -0.517.
A comparison of the CSI pH versus reference pH across all sites indicated that the
response was variable among test conditions. The CSI under reported pH by an average of 0.15,
0.40, and 0.68 pH units at Moss Landing, Chesapeake Bay, and the Great Lakes respectively. In
contrast the CSI over reported pH relative to the dye reference measurement by 0.22 for the
Hawaii field test.
Lastly, it is worth emphasizing that the continuous 15 – 30 minute time-series provided
by the test instrument was able to resolve a significantly greater dynamic range and temporal
resolution than could be obtained from discrete reference samples. Continuous in situ
monitoring technologies, such as the CSI, provide critical research and monitoring capabilities
for helping to understand and manage important environmental processes such as carbonate
chemistry and ocean acidification, as well as numerous other environmental or industrial
applications.